In the News
Lifetime Achievement Award
March 13, 2019
Wendy L. Freedman, John and Marion Sullivan University Professor in Astronomy and Astrophysics, University of Chicago
The Chicago Council on Science and Technology

Wendy Freedman is a renowned astronomer who was instrumental in precisely measuring the Hubble constant and determining the age of the universe. Freedman received both her BSc and PhD in astronomy and astrophysics from the University of Toronto. In 1984 she accepted a position as a postdoctoral fellow at the Carnegie Observatories in Pasadena, California. In 1987 Freedman became the first woman to join Carnegie's permanent staff, and in 2003 she became its director. She also initiated the Giant Magellan Telescope project and served as chair of its board of directors from the project's inception in 2003 until 2015. In 2014 she joined the faculty of the University of Chicago as the John and Marion Sullivan University Professor of Astronomy and Astrophysics. Freedman first rose to prominence leading the Hubble Space Telescope Key Project, which began in the mid-1980s and involved an international group of some 30 astronomers. The team used the Hubble telescope to study Cepheid variable stars in order to estimate intergalactic distances and thus determine the expansion rate of the universe.Learn more >>

Have Dark Forces Been Messing With the Cosmos?
February 27, 2019
by Dennis Overbye, The New York Times

Axions? Phantom energy? Astrophysicists scramble to patch a hole in the universe, rewriting cosmic history in the process.

Michael Turner, a veteran cosmologist at the University of Chicago and the organizer of a recent airing of the Hubble tensions, said, "Indeed, all of this is going over all of our heads. We are confused and hoping that the confusion will lead to something good!"Learn more >>

Edward 'Rocky' Kolb to direct Kavli Institute for Cosmological Physics
February 27, 2019
Prof. Rocky Kolb
Photo by Jason Smith
UChicago News

Cosmologist to lead center dedicated to study of origin and evolution of universe

The University of Chicago has named Edward W. 'Rocky' Kolb as director of its Kavli Institute for Cosmological Physics, a leading center dedicated to deepening our understanding of the origin and evolution of the universe and the laws that govern it.

Kolb, the Arthur Holly Compton Distinguished Service Professor in the Department of Astronomy and Astrophysics, succeeds Michael S. Turner as director, effective April 1. Turner, the Bruce V. & Diana M. Rauner Distinguished Service Professor in the Department of Astronomy and Astrophysics, has served in the role since 2010.

"We are thrilled that Rocky Kolb will lead KICP. Kolb, together with current KICP director Michael Turner, helped define a new discipline at the intersection of cosmology, particle physics and astrophysics," said Angela V. Olinto, dean of the Physical Sciences Division. "Kolb's extensive leadership experience will guarantee a brilliant future for KICP."

The institute was created as an interdisciplinary center to bridge astronomy and physics, exploring physics ranging from the subatomic scale to the birth and constitution of the cosmos. It is an international hub for cosmology and has furthered the careers of many young scientists.

At the institute, UChicago researchers tackle questions about the nature of dark energy and dark matter, the first moments of the universe, and nature's highest-energy particles. Members lead some of the most significant international astronomy projects in the field, such as the Dark Energy Survey, an unprecedented survey of distant galaxies to better understand the mysterious force accelerating the expansion of the universe; the South Pole Telescope, which with its third-generation camera will be among the most sensitive instruments observing the cosmic microwave background; and the Giant Magellan Telescope, a giant ground-based telescope under construction in Chile that is expected to produce images that are 10 times sharper than those from the Hubble Space Telescope.

"Rocky Kolb is an eminent cosmologist, known for his contributions to the study of the very early universe," said Kevin Moses, vice president of science programs at the Kavli Foundation. "He has had a distinguished career at the University of Chicago and Fermi National Accelerator Laboratory and is a longtime member of KICP. Rocky will continue the strong tradition of leadership at KICP, paving the way for further understanding of our cosmos."

Kolb is a fellow of the American Academy of Arts and Sciences and the American Physical Society. He has received numerous honors, including the Dannie Heineman Prize for Astrophysics, which he shared with Turner for their work to understand the early universe. Kolb has formerly served as dean of the Physical Sciences Division, chair of the Department of Astronomy and Astrophysics, and director of Fermi National Accelerator Laboratory's Particle Astrophysics Center.

The University established the Center for Cosmological Physics in 2001 with National Science Foundation support. The center was renamed the Kavli Institute for Cosmological Physics in 2004 in honor of Fred Kavli, who through the Kavli Foundation provided $7.5 million to endow the institute and support its programs.

UChicago's Kavli Institute works closely with the other Kavli Institutes in astrophysics at Stanford University, Peking University, Massachusetts Institute of Technology, University of California, Berkeley; and the University of Cambridge.Learn more >>

What's at the Edge of the Universe?
February 21, 2019
by Daniel Kolitz, Gizmodo

It is a routine emotion in 2019 to urgently wish, four or five times in a day, to be launched not simply into space but to the very edge of the universe, as far as it is possible to get from the fever dream of bad weather, busted trains and potentially cancerous thigh lesions that constitute life on Earth. But what would be waiting for you, up at the cosmological border? Is it even a border, or is what we're dealing with here more like a kind of inconceivably vast ceiling? Is there even a border/ceiling up there at all? For this week's Giz Asks, we talked with a number of cosmology-oriented physicists to find out.

Abigail Vieregg
Assistant Professor at the Kavil Institute for Cosmological Physics at the University of Chicago

Using telescopes on Earth, we look at light coming from distant places in the universe. The farther away the source of the light is, the longer it takes for that light to get here. So, when you look at far away places, you're looking at what those places were like when the light you saw was created - not at what those places are like today. You can keep looking farther and farther away, corresponding to farther and farther back in time, until you hit a place corresponding to a few hundred thousand years after the Big Bang. Before that, the universe was so hot and dense (well before there were stars and galaxies!) that any light in the universe just rattled around, and we can't see it with our telescopes today. This place is edge of the "observable universe" - sometimes called the horizon - because we can't see beyond it. As time goes on, this horizon changes. If you could look out from another planet somewhere else in the universe, presumably you would see something very similar to what we see here from Earth: your own horizon, limited by the time that has elapsed since the Big Bang, the speed of light, and the how the universe has expanded.

What does the place that corresponds to Earth's horizon today look like today? We can't know, since we can only view that place as it was just after the Big Bang, not as it is today. However, all the measurements indicate that all of the universe we can see, including the edge of the observable universe, looks approximately like our local universe does today: with stars, galaxies, and clusters of galaxies and lots of empty space.

We also think that the universe is much much bigger than the part of the universe we happen to be able to see here from Earth today, and there is no "edge" to the universe itself. It is just spacetime, expanding.

"All the measurements indicate that all of the universe we can see, including the edge of the observable universe, looks approximately like our local universe does today: with stars, galaxies, and clusters of galaxies and lots of empty space."Learn more >>

Big Brains podcast: "What Ripples in Space-Time Tell Us About the Universe with Daniel Holz"
January 24, 2019
Prof. Daniel Holz, KICP senior member
UChicago News

UChicago cosmologist discusses discovery of gravitational waves and colliding black holes

All around us in the universe, black holes are smashing into each other with tremendous force. These events are so powerful that they cause ripples in the fabric of space-time - and these ripples, called gravitational waves, travel hundreds of millions of light-years across the universe, eventually passing through the Earth.

Prof. Daniel Holz and fellow scientists at LIGO knew that detecting these waves would take us closer to figuring out many profound mysteries, including the size, age and composition of the universe. They built the most sensitive machine ever constructed, detected the waves and opened up an entirely new window on the universe.

In this time-and-space-bending episode of Big Brains, the UChicago cosmologist talks black holes, testing Einstein's predictions, and the threat of nuclear annihilation.Learn more >>

After mapping millions of galaxies, Dark Energy Survey finishes data collection
January 15, 2019
UChicago News

For the past six years, Fermi National Accelerator Laboratory has been part of an international effort to create an unprecedented survey of distant galaxies and better understand the nature of dark energy - the mysterious force accelerating the expansion of the universe.

After scanning about a quarter of the southern skies over 800 nights, the Dark Energy Survey finished taking data on Jan. 9. It ends as one of the most sensitive and comprehensive surveys of its kind, recording data from more than 300 million distant galaxies.

Fermilab, an affiliate of the University of Chicago, served as lead laboratory on the survey, which included more than 400 scientists and 26 institutions. The findings created the most accurate dark matter map of the universe ever made, shaping our understanding of the cosmos and its evolution. Other discoveries include the most distant supernova ever detected, a bevy of dwarf satellite galaxies orbiting our Milky Way, and helping to track the first-ever detection of gravitational waves from neutron stars back to its source.

According to Dark Energy Survey Director Rich Kron, a Fermilab scientist and professor at the University of Chicago, those results - and the scientists who made them possible - are where much of the real accomplishment of the Dark Energy Survey lies.

"The first generations of students and postdoctoral researchers on the Dark Energy Survey are now becoming faculty at research institutions and are involved in upcoming sky surveys," Kron said. "The number of publications and people involved are a true testament to this experiment. Helping to launch so many careers has always been part of the plan, and it's been very successful."

Now the job of analyzing that data takes center stage, providing opportunities for new breakthroughs. The survey has already released a full range of papers based on its first year of data, and scientists are now diving into the rich seam of catalogued images from the first several years of data, looking for clues to the nature of dark energy.

The first step in that process, according to Fermilab scientist Josh Frieman, a professor at UChicago and former director of the Dark Energy Survey, is to find the signal in all the noise.

"We're trying to tease out the signal of dark energy against a background of all sorts of non-cosmological stuff that gets imprinted on the data,' Frieman said. "It's a massive ongoing effort from many different people around the world."Learn more >>

Studying the stars with machine learning
November 12, 2018
Studying the stars with machine learning
by Evelyn Lamb, Symmetry Magazine

To keep up with an impending astronomical increase in data about our universe, astrophysicists turn to machine learning.

Kevin Schawinski had a problem.

In 2007 he was an astrophysicist at Oxford University and hard at work reviewing seven years' worth of photographs from the Sloan Digital Sky Survey - images of more than 900,000 galaxies. He spent his days looking at image after image, noting whether a galaxy looked spiral or elliptical, or logging which way it seemed to be spinning.

Technological advancements had sped up scientists' ability to collect information, but scientists were still processing information at the same rate. After working on the task full time and barely making a dent, Schawinski and colleague Chris Lintott decided there had to be a better way to do this.

There was: a citizen science project called Galaxy Zoo. Schawinski and Lintott recruited volunteers from the public to help out by classifying images online. Showing the same images to multiple volunteers allowed them to check one another's work. More than 100,000 people chipped in and condensed a task that would have taken years into just under six months.

Citizen scientists continue to contribute to image-classification tasks. But technology also continues to advance.

The Dark Energy Spectroscopic Instrument, scheduled to begin in 2019, will measure the velocities of about 30 million galaxies and quasars over five years. The Large Synoptic Survey Telescope, scheduled to begin in the early 2020s, will collect more than 30 terabytes of data each night - for a decade.

"The volume of datasets [from those surveys] will be at least an order of magnitude larger," says Camille Avestruz, a postdoctoral researcher at the University of Chicago.

To keep up, astrophysicists like Schawinski and Avestruz have recruited a new class of non-scientist scientists: machines.

Researchers are using artificial intelligence to help with a variety of tasks in astronomy and cosmology, from image analysis to telescope scheduling.

Superhuman scheduling, computerized calibration
Artificial intelligence is an umbrella term for ways in which computers can seem to reason, make decisions, learn, and perform other tasks that we associate with human intelligence. Machine learning is a subfield of artificial intelligence that uses statistical techniques and pattern recognition to train computers to make decisions, rather than programming more direct algorithms.

In 2017, a research group from Stanford University used machine learning to study images of strong gravitational lensing, a phenomenon in which an accumulation of matter in space is dense enough that it bends light waves as they travel around it.

Because many gravitational lenses can't be accounted for by luminous matter alone, a better understanding of gravitational lenses can help astronomers gain insight into dark matter.

In the past, scientists have conducted this research by comparing actual images of gravitational lenses with large numbers of computer simulations of mathematical lensing models, a process that can take weeks or even months for a single image. The Stanford team showed that machine learning algorithms can speed up this process by a factor of millions.

Schawinski, who is now an astrophysicist at ETH Zurich, uses machine learning in his current work. His group has used tools called generative adversarial networks, or GAN, to recover clean versions of images that have been degraded by random noise. They recently published a paper about using AI to generate and test new hypotheses in astrophysics and other areas of research.

Another application of machine learning in astrophysics involves solving logistical challenges such as scheduling. There are only so many hours in a night that a given high-powered telescope can be used, and it can only point in one direction at a time. "It costs millions of dollars to use a telescope for on the order of weeks," says Brian Nord, a physicist at the University of Chicago and part of Fermilab's Machine Intelligence Group, which is tasked with helping researchers in all areas of high-energy physics deploy AI in their work.Learn more >>

Gravitational waves could soon provide measure of universe's expansion
October 23, 2018
UChicago scientists estimate, based on LIGO's quick first detection of a first neutron star collision, that they could have an extremely precise measurement of the universe's rate of expansion within five to ten years.

Image by Robin Dienel/The Carnegie Institution for Science
by Louise Lerner, UChicago News

UChicago study: New LIGO readings could improve disputed measurement within 5-10 years

Twenty years ago, scientists were shocked to realize that our universe is not only expanding, but that it's expanding fasterover time.

Pinning down the exact rate of expansion, called the Hubble constant after famed astronomer and UChicago alumnus Edwin Hubble, has been surprisingly difficult. Since then scientists have used two methods to calculate the value, and they spit out distressingly different results. But last year's surprising capture of gravitational waves radiating from a neutron star collision offered a third way to calculate the Hubble constant.

That was only a single data point from one collision, but in a new paper published Oct. 17 in Nature, three University of Chicago scientists estimate that given how quickly researchers saw the first neutron star collision, they could have a very accurate measurement of the Hubble constant within five to ten years.

"The Hubble constant tells you the size and the age of the universe; it's been a holy grail since the birth of cosmology. Calculating this with gravitational waves could give us an entirely new perspective on the universe," said study author Daniel Holz, a UChicago professor in physics who co-authored the first such calculation from the 2017 discovery. "The question is: When does it become game-changing for cosmology?"

In 1929, Edwin Hubble announced that based on his observations of galaxies beyond the Milky Way, they seemed to be moving away from us - and the farther away the galaxy, the faster it was receding. This is a cornerstone of the Big Bang theory, and it kicked off a nearly century-long search for the exact rate at which this is occurring.

To calculate the rate at which the universe is expanding, scientists need two numbers. One is the distance to a faraway object; the other is how fast the object is moving away from us because of the expansion of the universe. If you can see it with a telescope, the second quantity is relatively easy to determine, because the light you see when you look at a distant star gets shifted into the red as it recedes. Astronomers have been using that trick to see how fast an object is moving for more than a century - it's like the Doppler effect, in which a siren changes pitch as an ambulance passes.Learn more >>

Gravitational waves provide dose of reality about extra dimensions
September 18, 2018
In new study, UChicago astronomers find no evidence for extra spatial dimensions to the universe based on gravitational wave data.

Courtesy of NASA's Goddard Space Flight Center CI Lab
by Louise Lerner, UChicago News

No evidence for extra spatial dimensions, UChicago scientists say

While last year's discovery of gravitational waves from colliding neutron stars was Earth-shaking, it won't add extra dimensions to our understanding of the universe -- not literal ones, at least.

University of Chicago astronomers found no evidence for extra spatial dimensions to the universe based on the gravitational wave data. Their research, published in the Journal of Cosmology and Astroparticle Physics, is one of many papers in the wake of the extraordinary announcement last year that LIGO had detected a neutron star collision.

The first-ever detection of gravitational waves in 2015, for which three physicists won the Nobel Prize last year, was the result of two black holes crashing together. Last year, scientists observed two neutron stars collide. The major difference between the two is that astronomers could see the aftermath of the neutron star collision with a conventional telescope, producing two readings that can be compared: one in gravity, and one in electromagnetic (light) waves.

"This is the very first time we've been able to detect sources simultaneously in both gravitational and light waves," said Prof. Daniel Holz. "This provides an entirely new and exciting probe, and we've been learning all sorts of interesting things about the universe."

Einstein's theory of general relativity explains the solar system very well, but as scientists learned more about the universe beyond, big holes in our understanding began to emerge. Two of these are dark matter, one of the basic ingredients of the universe; and dark energy, the mysterious force that's making the universe expand faster over time.

"This changes how a lot of people can do their astronomy."
- Astrophysicist Maya Fishbach

Scientists have proposed all kinds of theories to explain dark matter and dark energy, and "a lot of alternate theories to general relativity start with adding an extra dimension," said graduate student Maya Fishbach, a coauthor on the paper. One theory is that over long distances, gravity would "leak" into the additional dimensions. This would cause gravity to appear weaker, and could account for the inconsistencies.

The one-two punch of gravitational waves and light from the neutron star collision detected last year offered one way for Holz and Fishbach to test this theory. The gravitational waves from the collision reverberated in LIGO the morning of Aug. 17, 2017, followed by detections of gamma-rays, X-rays, radio waves, and optical and infrared light. If gravity were leaking into other dimensions along the way, then the signal they measured in the gravitational wave detectors would have been weaker than expected. But it wasn't.

It appears for now that the universe has the same familiar dimensions -- three in space and one of time -- even on scales of a hundred million light-years.

But this is just the beginning, scientists said. "There are so many theories that until now, we didn't have concrete ways to test," Fishbach said. "This changes how a lot of people can do their astronomy."

"We look forward to seeing what gravitational-wave surprises the universe might have in store for us," Holz said.

Other authors on the space-time study were Princeton's Kris Pardo and David Spergel.

Citation: "Limits on the number of space-time dimensions from GW170817." Pardo et al, Journal of Cosmology and Astroparticle Physics, July 23, 2018. doi: 10.1088/1475-7516/2018/07/048Learn more >>

New leaders from Fermilab appointed for Dark Energy Survey
September 16, 2018
Prof. Richard Kron, KICP senior associates
Fermilab News

On Oct. 1, Fermilab and University of Chicago scientist Rich Kron begins his three-year term as director of the Dark Energy Survey, or DES, hosted by Fermilab. Fellow Fermilab scientist Tom Diehl will serve as deputy director.

From 2003-2008, Kron was director of the Sloan Digital Sky Survey, an astronomical survey in which Fermilab was heavily engaged until 2008. In 2010, he stepped into the role of DES deputy director. Now, as incoming director, he succeeds Fermilab and University of Chicago scientist Josh Frieman, who became head of the Fermilab Particle Physics Division earlier this year.

The Dark Energy Survey is a multinational, collaborative effort to map hundreds of millions of galaxies and stars to better understand dark energy, the phenomenon behind the increasingly rapid expansion of the universe. Using a powerful camera installed on a telescope on a Chilean mountaintop, DES researchers are creating detailed maps of the southern sky to uncover patterns in the distribution of celestial objects that reflect - or reveal - the impact of dark energy on the formation of structure in the universe. They are also discovering and measuring properties of several thousand supernovae - distant exploding stars - to chart dark energy's influence on the history of cosmic expansion. The data will help researchers narrow in on dark energy's nature.

As the new DES director, Kron will lead the 400-strong collaboration through its final data-taking season, which runs from September 2018 to January 2019.

"I'm honored to be given the opportunity to lead the Dark Energy Survey to the conclusion of its operations and the production of the final science results," Kron said. "My predecessor Josh Frieman capably led the collaboration through the past eight years, and I have learned a lot from him."Learn more >>

Next-gen camera for South Pole Telescope takes data on early universe
September 13, 2018
The South Pole telescope is using its new third-generation camera to search for the oldest light in the universe.

Photo by Bradford Benson
by Louise Lerner , Jared Sagoff, UChicago News

UChicago-led collaboration installed sensitive new instrument in Antarctica

Deep in Antarctica, at the southernmost point on our planet, sits a 33-foot telescope designed for a single purpose: to make images of the oldest light in the universe.

This light, known as the cosmic microwave background, or CMB, has journeyed across the cosmos for 14 billion years - from the moments immediately after the Big Bang until now. Because it is brightest in the microwave part of the spectrum, the CMB is impossible to see with our eyes and requires specialized telescopes.

The South Pole Telescope, specially designed to measure the CMB, is using its third-generation camera to carry out a multi-year survey to observe the earliest instants of the universe. Since 2007, the SPT has shed light on the physics of black holes, discovered a galaxy cluster that is making stars at the highest rate ever seen, redefined our picture of when the first stars formed In the universe, provided new insights into dark energy and homed in on the masses of neutrinos. This latest upgrade improves its sensitivity by nearly an order of magnitude - making it among the most sensitive CMB instruments ever built.

"Being able to detect and analyze the CMB, especially with this level of detail, is like having a time machine to go back to the first moments of our universe," said John Carlstrom, the Subramanyan Chandrasekhar Distinguished Service Professor at UChicago and the principal investigator for the South Pole Telescope project.

"Encoded in images of the CMB light that we capture is the history of what that light has encountered in its 14-billion-year journey across the cosmos," he added. "From these images, we can tell what the universe is made up of, how the universe looked when it was extremely young and how the universe has evolved."

Located at the National Science Foundation's Amundsen-Scott South Pole Station, the telescope is operated by a collaboration of more than 80 scientists and engineers from a group of universities and U.S. Department of Energy national laboratories, including three institutions in the Chicago area. These research organizations - the University of Chicago, Argonne National Laboratory and Fermi National Accelerator Laboratory - have worked together to build a new, ultra-sensitive camera for the telescope, containing 16,000 specially manufactured detectors.

"The ability to operate a 10-meter telescope, literally at the end of the Earth, is a testament to the scientific capabilities of the researchers that NSF supports and the sophisticated logistical support that NSF and its partners are able to provide in one of the harshest environments on Earth," said Vladimir Papitashvili, Antarctic astrophysics and geospace sciences program director in NSF's Office of Polar Programs. "This new camera will extend the abilities of an already impressive instrument."

The telescope is funded and maintained by the National Science Foundation in its role as manager of the U.S. Antarctic Program, the national program of research on the southernmost continent.

'Baby pictures' of the cosmos
The CMB is the oldest light in our universe, produced in the intensely hot aftermath of the Big Bang before even the formation of atoms. These primordial particles of light, which have remained nearly untouched for nearly 14 billion years, provide unique clues about how the universe looked at the beginning of time and how it has changed since.

"This relic light is still incredibly bright - literally outshining all the stars that have ever existed in the history of the universe by over an order of magnitude in energy," said University of Chicago professor and Fermilab scientist Bradford Benson, who headed the effort to build this new camera.

However, because most of the energy is in the microwave part of the spectrum, to observe it we need to use special detectors at observatories in high and dry locations. The South Pole Station is better than anyplace else on Earth for this: it is located atop a two-mile thick ice sheet, and the extremely low temperatures in Antarctica mean there is almost no atmospheric water vapor.

"Built with cutting-edge detector technology, this new camera will significantly advance the search for the signature of early cosmic inflation in the cosmic microwave background and allow us to make inroads into other fundamental mysteries of the universe, including the masses of neutrinos and the nature of dark energy," said Kathy Turner of the Department of Energy's Office of Science.

Scientists are hoping to plumb this data for information on a number of physical processes and even new particles. "The cosmic microwave background is a remarkably rich source for science," Benson said. "The third-generation camera survey can give us clues on everything from dark energy to the physics of the Big Bang to locating the most massive clusters of galaxies in the universe."

"The cosmic microwave background is a remarkably rich source for science."
- Asst. Prof. Bradford Benson

The details of this "baby picture" of the cosmos will allow scientists to better understand the different kinds of matter and energy that make up our universe, such as neutrinos and dark energy. They may even find evidence of the gravitational waves from the beginning of the universe, regarded by many as the "smoking gun" for the theory of inflation.

It also serves as a rich astronomical survey; one of the things they'll be looking for are some of the first massive galaxies in the universe. These massive galaxies are increasingly of interest to astronomers as "star farms," forming the first stars in the universe, and since they are nearly invisible to typical optical telescopes, the South Pole Telescope is perhaps the most efficient way to find them.

'Nothing that comes out of a box'
The South Pole Telescope collaboration has operated the telescope since its construction in 2007. Grants from multiple sources - the National Science Foundation, the U.S. Department of Energy and the Kavli and Moore foundations - supported a second-generation polarization-sensitive camera. The latest third-generation focal plane contains ten times as many detectors as the previous experiment, requiring new ideas and solutions in materials and nanoscience.

"From a technology perspective, there is virtually nothing that comes 'out of a box,'" said Clarence Chang, an assistant professor at UChicago and physicist at Argonne involved with the experiment.

For the South Pole Telescope, scientists needed equipment far more sensitive than anything made commercially. They had to develop their own detectors, which use special materials for sensing tiny changes in temperature when they absorb light. These custom detectors were developed and manufactured from scratch in ultra-clean rooms at Argonne National Laboratory.

The detectors went to Fermilab to be assembled into modules, which included small lenses for each pixel made at the University of Illinois at Urbana-Champaign. After being tested at multiple collaborating universities around the country, the detectors made their way back to Fermilab to be integrated into the South Pole Telescope camera cryostat, designed by Benson. The camera looks like an 8-foot-tall, 2,500-pound optical camera with a telephoto lens on the front, but with the added complication that the lenses need to be cooled to just a few degrees above absolute zero. (Even Antarctic isn't that cold, so it needs this special cryostat to cool it down further.)

Finally, the new camera was ready for its 10,000-mile journey to Antarctica by way of land, air and sea. On the final leg, from NSF's McMurdo Station to the South Pole, it flew aboard a specialized LC130 cargo plane outfitted with skis so that it could land on snow near the telescope site, since the station sits atop an ice sheet. The components were carefully unloaded, and a team of more than 30 scientists raced to reassemble the camera during the brief three-month Antarctic summer - since the South Pole is not accessible by plane for most of the year due to temperatures that can drop to -100 F.

The South Pole Telescope's multi-year observing campaign brings together researchers from across North America, Europe and Australia. With the upgraded telescope taking data, the exploration of the cosmic microwave background radiation enters a new era with a powerful collaboration and an extremely sensitive instrument.

"The study of the CMB involves so many different kinds of scientific journeys," Chang said. "It's exciting to watch efforts from all over come together to push the frontiers of what we know."

The South Pole Telescope collaboration is led by the University of Chicago, and includes research groups at Argonne National Laboratory, Case Western Reserve University, Fermi National Accelerator Laboratory, Harvard-Smithsonian Astrophysical Observatory, Ludwig Maximilian University of Munich, McGill University, SLAC National Accelerator Laboratory, University of California at Berkeley, University of California at Davis, University of California at Los Angeles, University of Colorado at Boulder, University of Illinois at Urbana-Champaign, University of Melbourne and University of Toronto, as well as individual scientists at several other institutions.

The South Pole Telescope is funded primarily by the National Science Foundation's Office of Polar Programs and the U.S. Department of Energy Office of Science. Partial support also is provided by the NSF-funded Physics Frontier Center at the KICP, the Kavli Foundation, and the Gordon and Betty Moore Foundation.Learn more >>

Risa Wechsler Named Director of KIPAC
August 21, 2018
Risa Wechsler, former KICP fellow

Image credit: Dawn Harmer/SLAC National Accelerator Laboratory
The Kavli Foundation

Risa Wechsler has been appointed director of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint institute of the Department of Energy's SLAC National Accelerator Laboratory and Stanford University. On Sept. 15, she'll take over from Tom Abel, whose five-year term at the helm of the institute is coming to an end.

KIPAC was founded in 2003 to explore new frontiers in astrophysics and cosmology. As a joint institute of SLAC and Stanford, it brings together experts in theory, computation, experiments and observations - the combined power needed to answer fundamental questions about the universe.

Risa Wechsler, associate professor of physics and of particle physics and astrophysics at SLAC and Stanford, has been named third director of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC).

"KIPAC brought a completely new field of science to SLAC and Stanford," says SLAC Director Chi-Chang Kao. "Tom's leadership has been instrumental in raising the institution's profile. Risa's scientific excellence and experience will ensure KIPAC continues to grow and prosper."

Wechsler, an associate professor of physics at Stanford and of particle physics and astrophysics at SLAC, joined KIPAC in 2006. She became the head of the institute's theory group in 2009 and assistant director of scientific programs in 2013. From 2014 to 2018, Wechsler was co-spokesperson for the Dark Energy Spectroscopic Instrument Collaboration, and she has been chair of Stanford Physics Department's Committee on Equity and Inclusion since 2016. In 2017, she was named a fellow of the American Physical Society.

"In addition to being a highly regarded and accomplished researcher committed to outstanding science, Risa understands how the close partnership between Stanford and SLAC benefits both research and education in astrophysics and cosmology. She also recognizes the importance of supporting young talent in these disciplines," says Ann Arvin, vice provost and dean of research at Stanford. "KIPAC will thrive as a world-class research institute for the study of astrophysics and cosmology under her leadership."

Wechsler says, "This is an exciting time to be guiding KIPAC's future. We have a number of incredible research programs that will start taking data in the next five years. Those projects have been incubating for a long time, and soon we'll see the fruit of those many years of hard work. I'm also looking forward to broadening the scope of the astrophysics we do. New windows are opening on many aspects of the cosmos, from exoplanets to gravitational waves to galaxies farther away than any we've seen before, and they promise to greatly enrich our understanding of the universe over the next decade."

Wechsler, whose own research focuses on galaxy formation and cosmology using a combination of large simulations and galaxy surveys, hopes to strengthen connections with other academic units across the SLAC and Stanford campuses and leverage opportunities in data science, Earth science, engineering, and other areas. She points out that it's the people who make KIPAC what it is: "It has been a wonderful environment for young, exceptional scientists, and I believe we can make that environment even better."

She'll be the third KIPAC director, following Abel and Roger Blandford, the institute's founding director.

"Risa will be great for KIPAC," says Abel. "She knows it inside out and has been integral to making it what it is today. Her leadership will provide an exciting future and will help making KIPAC an even more fun and productive place to do research."Learn more >>

2018 APS Medal for Exceptional Achievement in Research
March 20, 2018
Photo credit: Kyle Bergner
APS News

The 2018 APS Medal for Exceptional Achievement in Research was awarded on February 1 to Eugene Parker, professor emeritus at the University of Chicago, for his "many fundamental contributions to space physics, plasma physics, solar physics, and astrophysics during the past 60 plus years." (Top Left) The medal was presented to Parker by 2018 APS President Roger Falcone along with APS CEO Kate Kirby. (Top Right) Family members and colleagues joined in the celebration: from left to right, Eric Parker, Susan Kane-Parker, Niesje Parker, Eugene Parker (seated); Michael Turner, Rocky Kolb, and Young-Kee Kim (University of Chicago), and Timothy Gay (University of Nebraska-Lincoln, APS Speaker of the Council, and University of Chicago Ph.D. graduate). APS is accepting nominations for the 2019 APS Medal now through May 1.Learn more >>

In 2017, a big year for science, we learned from cosmic discoveries
January 11, 2018
In 2017, a big year for science, we learned from cosmic discoveries
by Michael S. Turner, The Hill

Our Universe is unfathomably large - billions of years old, billions of light-years across, and filled with hundreds of billion of galaxies, each with hundreds of billions of stars and planets. It often is beyond the reach of our instruments and our minds. Nonetheless, driven by curiosity, each year we make discoveries that expand our view of it, surprise us and help us to understand our place within it.

The big event of 2017 was the collision of two neutron stars in a relatively nearby galaxy, 140 million light years away. Such events are commonplace, happening many times a day, yet this was one was special because for the first time, the National Science Foundation's Laser Interferometer Gravitational-wave Observatory (LIGO) detected tiny ripples in the fabric of space-time that the cataclysmic event created. LIGO alerted astronomers, and GW170817 became the most well-studied astrophysical event, viewed with radio, infrared, visible, x-ray and gamma-ray "eyes."

Here is but one thing we learned: most, if not all, of the heaviest elements in the periodic table, e.g., gold and platinum, were made by colliding neutron stars.

Of course, LIGO thrilled us in 2016 with its announcement that it had detected gravitational waves from colliding black holes; this past December, three American scientists (Barry Barish and Kip Thorne of Caltech, and Rainer Weiss of MIT) were honored with the Nobel Prize for that discovery.

Closer to home, in October we were surprised by the first interstellar asteroid ever seen. We are used to asteroids - debris left over from the formation of our solar system - visiting us. In fact, the PanSTARRS1 telescope on Haleakala that discovered Oumuamua (for "scout"), as it is now officially known, searches for near-Earth objects that are potentially Earth-threatening. Oumuamua is not bound to our sun; it flew in from the direction of the Lyra constellation, passed between Mercury and the sun, and flew out again in the direction of the Pegasus constellation.

As large as an aircraft carrier and similarly shaped, Oumuamua reminded us that we are connected to the rest of the cosmos. Our solar system likely has shed asteroids and even planets that have flown by other stars with planets, and four NASA spacecraft - Pioneers 10 and 11 and Voyagers 1 and 2 - have left our solar system. The Voyagers carry the Golden Record of sounds recorded from Earth that Carl Sagan and his team put together to introduce us to the larger Universe.

It has been more than 20 years since we discovered the first exoplanets (planets orbiting around other stars). NASA's Kepler satellite has been the exoplanet workhorse, having discovered more than 4,000 exoplanets and 600 planetary systems. Astronomers have identified around 10 exoplanets in the habitable zone. Last year's big news was the discovery of the TRAPPIST 1 system, seven terrestrial-like planets orbiting a red dwarf star about 40 light years away. Five of the seven planets are similar in size to Earth and three are in the habitable zone, the sweet spot where liquid water - and hopefully life - can exist. We are well on our way to answering a very big question: Are we alone?

Moving to the far reaches of the Universe, the most distant quasar seen yet was discovered last year. The light we see began the journey to us when the Universe was only about 700 million years old. It presents us with a mystery: How did the billion-solar-mass black hole that powers this quasar form so early in the history of the Universe? (All galaxies, including our Milky Way, have massive black holes at their centers and go through an early "quasar phase" when their black holes shine brightly because of infalling matter.) LIGO and other gravitational-wave detectors coming on line in the future should shed light on this question.

While the great American eclipse of 2017 was not a surprise and did not lead to any startling discoveries, millions of Americans including me - were awed by it as the path of totality traversed the United States from Oregon to Georgia. In this amazing natural phenomenon, the moon nicely fits over the sun and blocks its light, allowing us to look directly at the sun without being blinded and view its - beautiful corona.

The corona of the sun is much hotter (millions of degrees) and wispier than its surface, extending many solar radii beyond the disk of the sun. The corona is responsible for much of the sun's activity that impacts our planet, including solar flares and coronal mass ejections, and how the corona works is still a mystery. Later this year, NASA will launch the Parker Solar Probe, which will orbit the sun on a highly elliptical path that will take it inside the sun's corona - really! - more than 20 times to make measurements that could solve some of mysteries of the corona.

Science is now a global activity that the United States no longer dominates. But as these discoveries illustrate, we continue to lead. Our success has involved three critical elements: thinking bold, throwing deep and sticking with it.

The LIGO Nobel Laureates were bold enough to think that you could detect a change in distance of one-thousandth the size of a proton between two mirrors separated by four kilometers. The NSF threw deep when it invested close to $1 billion over 25 years to build LIGO. And NASA stuck with it when Hubble had initial mirror problems, and more recently when it found a work-around to keep Kepler producing science after two gyros failed at the end of its four-year planned mission.

Certainly, cosmic discoveries help us to understand our place in the Universe, but they also inspire and awe us, young and old.

Michael S. Turner is a theoretical cosmologist who coined the term "dark energy" in 1998. He is the Bruce V. and Diana M. Rauner Distinguished Service Professor at the University of Chicago, and is the former assistant director for mathematical and physical sciences for the National Science Foundation.Learn more >>

Colliding Neutron Stars Could Settle Cosmology's Biggest Controversy
October 26, 2017
by Natalie Wolchover, Quanta Magazine

Newly discovered "standard sirens" provide an independent, clean way to measure how fast the universe is expanding.

To many cosmologists, the best thing about neutron-star mergers is that these events scream into space an otherwise close-kept secret of the universe. Scientists combined the gravitational and electromagnetic signals from the recently detected collision of two of these stars to determine, in a cleaner way than with other approaches, how fast the fabric of the universe is expanding -- a much-contested number called the Hubble constant.

In the days since the neutron-star collision was announced, Hubble experts have been surprised to find themselves discussing not whether events like it could settle the controversy, but how soon they might do so.

Scientists have hotly debated the cosmic expansion rate ever since 1929, when the American astronomer Edwin Hubble first established that the universe is expanding -- and that it therefore had a beginning. How fast it expands reflects what's in it (since matter, dark energy and radiation push and pull in different ways) and how old it is, making the value of the Hubble constant crucial for understanding the rest of cosmology.

And yet the two most precise ways of measuring it result in different answers, with a curious 8 percent discrepancy that "is currently the biggest tension in cosmology," said Dan Scolnic of the University of Chicago's Kavli Institute for Cosmological Physics. The mismatch could be a clue that cosmologists aren't taking into account important details that have affected the universe's evolution. But to see if that's the case, they need an independent check on the measurements.

Neutron-star collisions -- newly detectable by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo detectors -- seem to be just the thing.

"This first [collision] gives us a seat at the cosmology table," Daniel Holz, an astrophysicist with the University of Chicago and LIGO who was centrally involved in the new Hubble measurement, said in an email. "And as we get more, we can expect to play a major role in the field."

In an expanding universe, the farther away an astronomical object is, the faster it recedes. The Hubble constant says how much faster. Edwin Hubble himself estimated that galaxies move away from us 500 kilometers per second faster for each additional megaparsec of distance between us and them (a megaparsec is about 3.3 million light-years). This was a gross overestimate; by the 1970s, astrophysicists favored values for the Hubble constant around either 50 or 100 kilometers per second per megaparsec, depending on their methods. As errors were eliminated, these camps met near the middle. However, in the past year and a half, the Hubble trouble has reheated. This time, 67 stands off against 73.

The higher estimate of 73 comes from observing lots of astronomical objects and estimating both distance and velocity for each one. It's relatively easy to see how fast a star or galaxy is receding by looking at its "redshift" -- a reddening in color that happens for the same reason the sound of a receding ambulance's siren drops in pitch. Correct for an object's "peculiar velocity," caused by the gravitational pull of other objects in its neighborhood, and you're left with its recessional velocity due to cosmic expansion.

Historically, however, it has proven much, much harder to measure the distance to an object -- the other data point needed to calculate the Hubble constant.

To gauge how far away things are, astronomers build up rungs on a "cosmic distance ladder" in which each rung calibrates more-distant rungs. They start by deducing the distances to stars in the Milky Way using parallax -- the stars' apparent motion across the sky over the course of the year. With this information, astronomers can deduce the brightness of so-called Cepheid stars, which can be used as so-called "standard candles" because they all shine with a known intrinsic brightness. They then spot these Cepheid stars in nearby galaxies and use them to calculate how far away the galaxies must be. Next, the Cepheids are used to calibrate the distances to Type Ia supernovas -- even brighter (though rarer) standard candles that can be seen in faraway galaxies.

Each jump from one rung to the next risks miscalculation. And yet, in 2016, a team known as SH0ES used the cosmic distance ladder approach to peg the Hubble constant at 73.2 with an accuracy of 2.4 percent.

However, in a paper published the same year, a team used the Planck telescope's observations of the early universe to obtain a value of 67.8 for the current expansion rate -- supposedly with 1 percent accuracy.

The Planck team started from the faint drizzle of ancient light called the cosmic microwave background (CMB), which reveals the universe as it looked at a critical moment 380,000 years after the Big Bang. The CMB snapshot depicts a simple, nearly smooth, plasma-filled young universe. Pressure waves of all different wavelengths rippled through the plasma, squeezing and stretching it and creating subtle density variations on different length scales.

At the moment recorded in the CMB, pressure waves with particular wavelengths would have undergone just the right fraction of an undulation since the Big Bang to all reach zero amplitude, momentarily disappearing and creating smooth plasma densities at their associated length scale. Meanwhile, pressure waves with other wavelengths undulated just the right amount to exactly peak in amplitude at the critical moment, stretching and squeezing the plasma to the full extent possible and creating maximum density variations at their associated scales.

These peaks and troughs in density variations at different scales, which can be picked up by telescopes like Planck and plotted as the "CMB power spectrum," encode virtually everything about the young universe. The Hubble constant, in particular, can be reconstructed by measuring the distances between the peaks. "It's a geometric effect," explained Leo Stein, a theoretical physicist at the California Institute of Technology: The more the universe has expanded, the more the light from the CMB has curved through expanding space-time, and the closer together the peaks ought to appear to us.

Other properties of nature also affect how the peaks end up looking, such as the behavior of the invisible "dark energy" that infuses the fabric of the cosmos. The Planck scientists therefore had to make assumptions about all the other cosmological parameters in order to arrive at their estimate of 67 for the Hubble constant.

The similarity of the two Hubble measurements "is amazing" considering the vastly different approaches used to determine them, said Wendy Freedman, an astrophysicist at the University of Chicago and a pioneer of the cosmic distance ladder approach. And yet their margins of error don't overlap. "The universe looks like it's expanding about eight percent faster than you would have expected based on how it looked in its youth and how we expect it to evolve," Adam Riess of Johns Hopkins University, who led the SH0ES team, told Scientific American last year. "We have to take this pretty darn seriously."

The 67-versus-73 discrepancy could come down to an unknown error on one side or both. Or it might be real and significant -- an indication that the Planck team's extrapolation from the early universe to the present is missing a cosmic ingredient, one that changed the course of history and led to a faster expansion rate than otherwise expected. If a hypothesized fourth type of neutrino populated the infant universe, for instance, this would have increased the radiation pressure and affected the CMB peak widths. Or dark energy, whose repulsive pressure accelerates the universe's expansion, might be getting denser over time.

Suddenly, neutron-star collisions have materialized to cast the deciding vote.

The crashing stars serve as "standard sirens," as Holz and Scott Hughes of the Massachusetts Institute of Technology dubbed them in a 2005 paper, building on the work of Bernard Schutz 20 years earlier. They send rushes of ripples outward through space-time that are not dimmed by gas or dust. Because of this, the gravitational waves transmit a clean record of the strength of the collision, which allows scientists to "directly infer the distance to the source," Holz explained. "There is no distance ladder, and no poorly understood astronomical calibrations. You listen to how loud the [collision] is, and how the sound changes with time, and you directly infer how far away it is." Because astronomers can also detect electromagnetic light from neutron-star collisions, they can use redshift to determine how fast the merged stars are receding. Recessional velocity divided by distance gives the Hubble constant.

From the first neutron-star collision alone, Holz and hundreds of coauthors calculated the Hubble constant to be 70 kilometers per second per megaparsec, give or take 10. (The major source of uncertainty is the unknown angular orientation of the merging neutron stars relative to the LIGO detectors, which affects the measured amplitude of the signal.) Holz said, "I think it's just pure luck that we're smack in the middle," between the cosmic-distance-ladder and cosmic-microwave-background Hubble estimates. "We could easily shift to one side or the other."

The measurement's accuracy will steadily improve as more standard sirens are heard over the next few years, especially as LIGO continues to ramp up in sensitivity. According to Holz, "With roughly 10 more events like this one, we'll get to 1 percent [of error]," though he stresses that this is a preliminary and debatable estimate. Riess thinks it will take more like 30 standard sirens to reach that level. It all depends on how lucky LIGO and Virgo got with their first detection. "I do think the method has the potential to be a game changer," said Freedman. "How fast this will occur [or] what the rate of these objects will be ... we don't yet know."

Scolnic, who was part of SH0ES, said his team's tension with Planck's measurement is so large that "the standard siren approach doesn't need to get to 1 percent to be interesting."

As more standard sirens resound, they'll gradually home in on the Hubble constant once and for all and determine whether or not the expansion rate agrees with expectations based on the young universe. Holz, for one, is exhilarated. "I've dedicated the last decade of my life in the hopes of making one plot: a standard siren measurement of the Hubble. I got to make my Hubble plot, and it is beautiful."Learn more >>

Eclipse reflects sun's historic power
August 16, 2017
Michael Turner, KICP director
UChicago News

Eclipses have fascinated people since the earliest days of recorded history.

These rare astronomical events have helped explain the world around us -- from ancient Mesopotamia, where they were believed to foretell the deaths of kings, all the way to the 20th century, when they helped prove Einstein's theory of general relativity.

Such interest hasn't dimmed. People across the United States will have an opportunity on Aug. 21 to witness the first total solar eclipse from coast to coast in 99 years. UChicago faculty and students are among the hordes of enthusiasts traveling across the country toward the area of "totality," the 70-mile-wide stripe stretching from Oregon to South Carolina in which the moon will fully block the sun.

Ahead of this historic event, UChicago News asked scholars in fields ranging from theoretical cosmology to Islamic studies to discuss eclipses and their power.

The eclipse that proved Einstein was right
Michael Turner, Bruce V. & Diana M. Rauner Distinguished Service Professor in Physics

"Astronomers have learned a lot from eclipses, including one in 1919 that proved Einstein was right.

At the time, only a handful of people were aware of general relativity; Sir Arthur Eddington was one of them. He led an eclipse expedition into the Atlantic to find out whether gravity would bend starlight, as predicted by general relativity. What you want to do is look at stars very close to the sun, and see whether the light coming toward us is bent by the sun's gravity. With the moon blocking the sun, you can get that measurement, and it was exactly what Einstein predicted. The scientific community was agog. It instantly put general relativity on the map, and made Einstein a rockstar.

We're still learning things from eclipses. One thing people will study during this event is the corona of the sun, which is the glowing aura of gases that surrounds the sun. There are still things we don't understand about it -- such as exactly why it actually burns hundreds of times hotter than the surface of the sun itself.

A few years from now, NASA will launch a probe named after UChicago's own Eugene Parker that will explore the sun's corona -- closer than any probe has ever come to the sun."Learn more >>

New sky survey shows that dark energy may one day tear us apart
August 7, 2017
Measurements reveal a mismatch.
Image credit: Reidar Hahn, Fermilab
by Shannon Hall, New Scientist

The fate of the universe just became a little less certain. That's due to a disagreement between a map of the early universe and a new map of today's universe. If the mismatch stands the test of future measurements, we might have to rewrite physics. But that is a pretty big if.

The new results, which are part of the ongoing Dark Energy Survey (DES), charted the distribution of matter across 26 million galaxies in a large swathe of the southern sky.

"This is one of the most powerful pictures of the universe today that we've ever had," says Daniel Scolnic at the University of Chicago, who is a part of the 400-person DES collaboration but wasn't involved in this work.

It is so powerful because knowing the distribution, or clumpiness, of galaxies helps us better understand the cosmic game of tug of war as dark energy - a mysterious force that causes the universe to accelerate - pulls each galaxy apart, and dark matter - a theoretical but still unseen form of matter - pushes each galaxy together.Learn more >>

Ever-Elusive Neutrinos Spotted Bouncing Off Nuclei for the First Time
August 4, 2017
SNS's Beamline 13, which carries neutrons from the SNS collider to experimental stations. The same process that produces the neutrons also spits out neutrinos, which enter the COHERENT detector in the SNS basement.
Credit: Jean Lachat University of Chicago.
by Jesse Dunietz, Scientific American

A new technology for detecting neutrinos represents a "monumental" advance for science.

Juan Collar, a professor in physics at the University of Chicago, with a prototype of the world's smallest neutrino detector used to observe for the first time an elusive interaction known as coherent elastic neutrino nucleus scattering.

Neutrinos are famously antisocial. Of all the characters in the particle physics cast, they are the most reluctant to interact with other particles. Among the hundred trillion neutrinos that pass through you every second, only about one per week actually grazes a particle in your body.

That rarity has made life miserable for physicists, who resort to building huge underground detector tanks for a chance at catching the odd neutrino. But in a study published today in Science, researchers working at Oak Ridge National Laboratory (ORNL) detected never-before-seen neutrino interactions using a detector the size of a fire extinguisher. Their feat paves the way for new supernova research, dark matter searches and even nuclear nonproliferation monitoring.

Under previous approaches, a neutrino reveals itself by stumbling across a proton or neutron amidst the vast emptiness surrounding atomic nuclei, producing a flash of light or a single-atom chemical change. But neutrinos deign to communicate with other particles only via the "weak" force -- the fundamental force that causes radioactive materials to decay. Because the weak force operates only at subatomic distances, the odds of a tiny neutrino bouncing off of an individual neutron or proton are miniscule. Physicists must compensate by offering thousands of tons of atoms for passing neutrinos to strike.

The new experimental collaboration, known as COHERENT, instead looks for a phenomenon called CEvNS (pronounced "sevens"), or coherent elastic neutrino-nucleus scattering. CEvNS relies on the quantum mechanical equivalence between particles and waves, comparable to ocean waves. The high-energy neutrinos sought by most experiments are like short, choppy ocean waves. When such narrow waves pass under floating debris, they can pick out one leaf or twig at a time to toss around. Similarly, a high-energy neutrino typically picks out individual protons and neutrons with which to interact. But just as a long, slow wave would pick up the whole patch of debris at once, a low-energy neutrino sees the entire atomic nucleus as one "coherent" whole. This dramatically improves the odds of an interaction. As the number of neutrons in the nucleus is increased, the effective target size for the neutrino to hit grows in lockstep not just with that number, but with its square.Learn more >>

World's smallest neutrino detector observes elusive interactions of particles
August 4, 2017
Prof. Juan Collar led a team of UChicago physicists who built a lightweight, portable neutrino detector to observe the elusive interactions of the ghostly particles.
by Steve Koppes, UChicago News

UChicago physicists play leading role in confirming theory predicted four decades ago

In 1974, a Fermilab physicist predicted a new way for ghostly particles called neutrinos to interact with matter. More than four decades later, a UChicago-led team of physicists built the world's smallest neutrino detector to observe the elusive interaction for the first time.

Neutrinos are a challenge to study because their interactions with matter are so rare. Particularly elusive has been what's known as coherent elastic neutrino-nucleus scattering, which occurs when a neutrino bumps off the nucleus of an atom.

The international COHERENT Collaboration, which includes physicists at UChicago, detected the scattering process by using a detector that's small and lightweight enough for a researcher to carry. Their findings, which confirm the theory of Fermilab's Daniel Freedman, were reported Aug. 3 in the journal Science.

"Why did it take 43 years to observe this interaction?" asked co-author Juan Collar, UChicago professor in physics. "What takes place is very subtle." Freedman did not see much of a chance for experimental confirmation, writing at the time: "Our suggestion may be an act of hubris, because the inevitable constraints of interaction rate, resolution and background pose grave experimental difficulties."

When a neutrino bumps into the nucleus of an atom, it creates a tiny, barely measurable recoil. Making a detector out of heavy elements such as iodine, cesium or xenon dramatically increases the probability for this new mode of neutrino interaction, compared to other processes. But there's a trade-off, since the tiny nuclear recoils that result become more difficult to detect as the nucleus grows heavier.

"Imagine your neutrinos are ping-pong balls striking a bowling ball. They are going to impart only a tiny extra momentum to this bowling ball," Collar said.

To detect that bit of tiny recoil, Collar and colleagues figured out that a cesium iodide crystal doped with sodium was the perfect material. The discovery led the scientists to jettison the heavy, gigantic detectors common in neutrino research for one similar in size to a toaster.

No gigantic lab
The 4-inch-by-13-inch detector used to produce the Science results weighs only 32 pounds (14.5 kilograms). In comparison, the world's most famous neutrino observatories are equipped with thousands of tons of detector material.

"You don't have to build a gigantic laboratory around it," said UChicago doctoral student Bjorn Scholz, whose thesis will contain the result reported in the Science paper. "We can now think about building other small detectors that can then be used, for example to monitor the neutrino flux in nuclear power plants. You just put a nice little detector on the outside, and you can measure it in situ."

Neutrino physicists, meanwhile, are interested in using the technology to better understand the properties of the mysterious particle.

"Neutrinos are one of the most mysterious particles," Collar said. "We ignore many things about them. We know they have mass, but we don't know exactly how much."

Through measuring coherent elastic neutrino-nucleus scattering, physicists hope to answer such questions. The COHERENT Collaboration's Science paper, for example, imposes limits on new types of neutrino-quark interactions that have been proposed.

The results also have implications in the search for Weakly Interacting Massive Particles. WIMPs are candidate particles for dark matter, which is invisible material of unknown composition that accounts for 85 percent of the mass of the universe.

"What we have observed with neutrinos is the same process expected to be at play in all the WIMP detectors we have been building," Collar said.

Neutrino alley
The COHERENT Collaboration, which involves 90 scientists at 18 institutions, has been conducting its search for coherent neutrino scattering at the Spallation Neutron Source at Oak Ridge National Laboratory in Tennessee. The researchers installed their detectors in a basement corridor that became known as "neutrino alley." This corridor is heavily shielded by iron and concrete from the highly radioactive neutron beam target area, only 20 meters (less than 25 yards) away.

This neutrino alley solved a major problem for neutrino detection: It screens out almost all neutrons generated by the Spallation Neutron Source, but neutrinos can still reach the detectors. This allows researchers to more clearly see neutrino interactions in their data. Elsewhere they would be easily drowned out by the more prominent neutron detections.

The Spallation Neutron Source generates the most intense pulsed neutron beams in the world for scientific research and industrial development. In the process of generating neutrons, the SNS also produces neutrinos, though in smaller quantities.

"You could use a more sophisticated type of neutrino detector, but not the right kind of neutrino source, and you wouldn't see this process," Collar said. "It was the marriage of ideal source and ideal detector that made the experiment work."

Two of Collar's former graduate students are co-authors of the Science paper: Phillip Barbeau, AB'01, SB'01, PhD'09, now an assistant professor of physics at Duke University; and Nicole Fields, PhD'15, now a health physicist with the U.S. Nuclear Regulatory Commission in Chicago.

The development of a compact neutrino detector brings to fruition an idea that UChicago alumnus Leo Stodolsky, SM'58, PhD'64, proposed in 1984. Stodolsky and Andrzej Drukier, both of the Max Planck Institute for Physics and Astrophysics in Germany, noted that a coherent detector would be relatively small and compact, unlike the more common neutrino detectors containing thousands of gallons of water or liquid scintillator. In their work, they predicted the arrival of future neutrino technologies made possible by the miniaturization of the detectors.

Scholz, the UChicago graduate student, saluted the scientists who have worked for decades to create the technology that culminated in the detection of coherent neutrino scattering.

"I cannot fathom how they must feel now that it's finally been detected, and they've achieved one of their life goals," Scholz said. "I've come in at the end of the race. We definitely have to give credit to all the tremendous work that people have done before us."Learn more >>

Dark Energy Survey reveals most accurate measurement of dark matter structure in the universe
August 3, 2017
Composite picture of stars over the Cerro Tololo Inter-American Observatory in Chile.
Photo: Reidar Hahn/Fermilab
Fermilab News

Imagine planting a single seed and, with great precision, being able to predict the exact height of the tree that grows from it. Now imagine traveling to the future and snapping photographic proof that you were right.

If you think of the seed as the early universe, and the tree as the universe the way it looks now, you have an idea of what the Dark Energy Survey (DES) collaboration has just done. In a presentation today at the American Physical Society Division of Particles and Fields meeting at the U.S. Department of Energy's (DOE) Fermi National Accelerator Laboratory, DES scientists will unveil the most accurate measurement ever made of the present large-scale structure of the universe.Learn more >>